SAT673 Novel Mutation Of TBX3 Associated With Morbid Obesity In Human

Disclosure: H.R. Alkaissi: None. B. Ji: None. S. McFarlane: None. Background: TBX3 is a transcription involved in the development of the heart conduction system, apocrine and mammary glands, limbs, and lung development and maturation, with variable oncogenic roles. Recently, the role of TBX3 and body weight control has been demonstrated in animal models, showing an essential role for TBX3 in hypothalamic arcuate neuronal maturation, function, and identity [1]. Case: 26-year-old woman referred for the management of morbid obesity and menstrual irregularities. The patient weighed 330 lbs, with a BMI of 55 kg/m(2), with hypertension T2DM. The patient had a normal development until age five, after which she experienced regression in milestones and lost the ability to communicate, and was diagnosed with autism. She had a history of food-seeking behavior, leading to progressive weight gain, which was managed by blocking access to food, such as locking the fridge. The patient's weight fluctuated from 290 lbs to 330 lbs. Family history of T2DM in her maternal relatives. She was diagnosed with T2DM at the age of 18, with HbA1c level of 9.4%. Autoantibody testing was negative for glutamic acid decarboxylase (GAD), islet cell antibody (ICA), and zinc transporter 8 (ZnT8). The fasting C-peptide level was detectable at 1.87 ng/mL. T2DM was well controlled with an HbA1C range of 6.0-6.7% with the use of short and long-acting insulin regimen. However, with improved glycemic control, short-acting insulin was stopped and she was started on liraglutide. Syndromic obesity was suspected due to early-onset of the disease and the developmental regression. Testing for Prader-Willi syndrome was negative, based on a normal chromosome 15 methylation study. Leptin levels were elevated at 66 ng/mL, prompting further testing for obesity-related genetic mutations. Next-generation sequencing and targeted Sanger sequencing for 79 genes associated with obesity in human and animal models was performed. A novel mutation was identified in TBX3 activation domain, c. C1513T (p.P505S). UniProt peptide sequence alignment analyzed for sequence conservation. ClinVar, HGMD and GWAS Catalogue databases screened for similar variants. Discussion: We present the first case in human, where novel TBX3 mutation results in hypothalamic dysfunction, leptin resistance manifesting as morbid obesity, hyperphagia, and menstrual irregularities. The reported mutation in the activation domain (A) of TBX3. In silico analysis showed high evolutionary conservation of the mutated domain (across vertebrate species), indicating the mutation is likely pathogenic. References:1. Quarta C, Fisette A, Xu Y, et al. Functional identity of hypothalamic melanocortin neurons depends on Tbx3. Nat Metab. 2019 Feb;1(2):222-235. doi: 10.1038/s42255-018-0028-1. Epub 2019 Jan 28. PMID: 32694784; PMCID: PMC8291379. Presentation: Saturday, June 17, 2023